Yosemite's Lyell Glacier, second-largest in the Sierras, has lost 80% of its surface area, down to .27 square km. Wiki says it's split in two and not moving, arguably not a glacier anymore, just stagnant ice.
I tried to get up to this one a year back but it didn't work out. Still on my list.
Glaciers can come back though. About 20 rash years ago, I was glissading down what was supposed to be a snowfield and not a glacier in Alaska when I found myself sliding toward a crevasse. I couldn't stop but I got my feet underneath me and jumped it (it wasn't very wide). That's when I learned that small glaciers can come and go, although the global trend for glaciers is obvious enough.